Alternating-current motor system.



PATENTED NOV. 21, 1905.

A. G. DAVIS. ALTERNATING CURRENT MOTOR SYSTEM.

APPLICATION FILED APR. 9, 1902.

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No. 805,415. PATENTED NOV. 21, 1905. A. G. DAVIS. ALTERNATING CURRENT MOTOR SYSTEM.

APPLICATION FILED APR. 9, 1902.

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PATENTED NOV. 21, 1905.

A. G. DAVIS.

ALTERNATING CURRENT MOTOR SYSTEM.

APPLICATION FILED APR. 9, 1902.

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PATENTED NOV. 21, 1905.

A. G. DAVIS. ALTBRNATING CURRENT MOTOR SYSTEM.

APPLICATION FILED APR. 9, 1902.

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UNITED STATES PATENT OFFICE.

ALBERT G. DAVIS, OF SCI-IENECTADY, NEW YORK, ASSIGNOR TO GEN- ERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ALTERNATlNG-CURRENT MOTOR SYSTEM.

Specification of Letters Patent.

Patented NOV. 21, 1905.

Original application filed April 4, 1893, Serial No. 676,306. Divided and this application filed April 9,1902. Serial No. 102,01et.

To all whom it may concern.-

Be it known that I, ALBERT G. DAVIS, acitizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Alternating-Current Motor Systems, (division of my prior application, Serial No. 676,306, filed April 4, 1898,) of which the following is a specification.

My invention relates to alternating-current motor systems, and particularly to those of the tandem and tandem-multiple types, and is designed to provide an arrangement whereby such a motor system may be started with full torque and run efliciently at various speeds.

One important function of my invention consists in connecting in tandem with a single-phase alternating-current motor actually driving a load a multiphase alternating-current motor also driving a load, which may be the same load as that driven by the first motor. For example, both motors may be connected to the same or different axles of a street-car. Further, my invention contemplates regulating the speed of the system thus formed in various ways and thereafter connecting the motors in tandem across the single-phase mains. In this way I am able to drive a regulable and self-starting motor system possessing the advantages of a multiphase tandem-multiple system from a source of single-phase current which is particularly valuable in connection with railway-work.

My invention also comprises certain means for varying the resistance of the induced member of one or more of the motors, which is particularly useful when the change from tandem to multiple is made.

My invention also comprises a method of neutralizing or adjusting the phase displacement in the intermediate circuits of a tandem or tandem-multiple system or in any multiphase system whatever and various other combinations and arrangements of parts and connections to be hereinafter more fully described and claimed.

I have illustrated various embodiments of my invention in the accompanying drawings, in which Figure 1 is a general diagrammatic view of a motor system constructed and arranged in accordance with my invention and applied to railway-work. Fig. 2 is a section on the line 22 of Fig. 3, and Fig. 3 is a section on the line 3 3 of Fig. 2, both sections showing details of the means for varying the armature resistance in its preferred form. Fig. 4 is a development of the induced member of one of the motors, showing diagrammatically the resistance-varying means. Figs. 5, 6, 7, 8, 9, 10, and 11 are diagrams illustrating the circuit relations of my improved system for various controller positions, and Fig. 12 shows one form of my improved means for neutralizing the self-induction and regulating the phase of the intermediate circuits.

Referring more particularly to Fig. 1, A B are the two motors shown as connected to a common shaft S. A B are the inducing members, and A B are the induced members, the relations of the parts being reversed in the two motors. H is a generator of single-phase alternating currents shown as feeding current through a tension raising transformer T, transmission-lines 1 1, and a tension-red ucing transformer T to the trolley or third rail L and the track-rail R. Connection to the car is made through the trolley t and the wheels W, as usual, though obviously any other suitable arrangement may be substituted. The motor A is provided with a flux-screen A independently rotatable in the airgap and containing a short circuited winding, as shown. As is well known in the art, if the flux-screen be set in rotation it will so distort the flux set up by the current flowing in the primary single-phase circuit shown on the member A as to produce in the induced member A a rotary field. This rotary field generates dephased electromotive forces in the winding of the induced member A which winding may be of any well-known type and should preferably be similar in arrangement to the windings of any ordinary multiphase generator-armature. The electromotive forces so generated cause multiphase current to flow in the circuits leading from the rings and brushes. These currents are led through condensers C C to the inducing member B of the motor .B, in which member they produce a rotary field. This rotary field in turn generates current in the induced member B which reacts to create torque. It will thus be seen that both motors produce a rotary effort at the start and tend to run to such a speed that the frequency of the current in the intermediate circuit in which the phase-advancing devices are preferably interposed is nearly one-half of the frequency of the current fed to the primary of the first motor A.

To start the flux-screen A", I provide a small auxiliary motor M, which, as it is of insignificant output, may be of the split-phase type, as shownthat is to say, it may be Wound like an ordinary two-phase or threephase motor and provided with a monocyclic starting device consisting of a self-induction M and a condenser or resistance M, as shown. The armature M of this motor drives the flux-screen A through a belt D, pulleys E F, and a second belt G. The magnets M M serve when energized by the battery 6 or other source of current to reduce the resistance of the induced members of the motors A and B, respectively, preferably by the arrangement to be hereinafter described.

To start the motors, the controller K (here shown in development only) is shown so that the brushes 10 to 36, inclusive, bear upon the line 1. Current then flows from the trolley 16 through brush 13 to contact-plate 13 and brush 15 to the motor M and thence to brush 12, by contact 1O to brush 10, and to ground through the wheels 1V. It will be seen that this position simply acts to start the small motor M and the flux-screen A The connections are indicated in diagram in Fig. 5, in which it will be seen that the primary of the motor 1W1 is energized and the secondary short-circuited upon itself, while the windings of the other members A A B B are deenergized. When the flux-screen has attained a sufficient spee l, the controller is moved to the second position 2. Here contacts 13" and 10 are energized, as before, by the brushes 13 and 10, so that current flows from contact 13*, through brush 14, to the primary winding A, through the brush 11, and to the con tact 10. This generates an alternating flux in the member A, which is converted into a rotary fiuX by the action of the flux-screen A which now, since it drives no appreciable load, runs up to a speed approaching that of synchronism. The rotary field thus induced in the secondary A causes dephased currents to be generated in the multiphase winding of that member, supposed in this case to be a two-phase winding. Current then flows from the brush a to the condenser C and thence through the first section of the condenser to the contact 16 and brush 19, thence to the brush Z) of the motor B, and through the winding B to the brush U, to brush 21, to the controller-contact 2O and brush 20, back to the motor A at the brush a The other intermediate circuit is from the brush a to the condenser C, brush 22, contact 22, brush 25, motor-brush 6 through the inducing member B, to the brush 6*, brush 27 and contact 26, and thence to the brush a" on the motor A. The current passing in these paths will create a rotary field in the inducing member B, which may be wound, as shown, with soaais a ring winding tapped at four equidistant points, or with two independent circuits, or in any other suitable way. This rotary lield will produce electromotive forces in the bars of the winding B which in turn will produce currents in these bars, which bars are arranged in two circuits and constitute an ordinary multiphase secondary. The terminals of these two circuits lead, respectively, to brushes 28 29 and 30 31, which brushes are united together in pairs by the resistances R R. It will thus be seen thatin this position, which is illustrated in diagram in Fig. 6, the motor M is energized, the primary A is also energized with single-phase current, and the primary B of the motorB is fed with quarterphase current from the secondary A of the motor A through the condensers C C, while the secondary B of the motor B is closed on itself through resistances R R The position above described is the starting position. The current flowing in the intermediate circuits of the tandem system is in general of a frequency equal to the slip of the motor A, which slipis, before the motor starts, equal to the frequency of the original current; but as the motor A starts the frequency of the current in the intermediate circuit falls, as is well understood. hen a small speed has been attained, the controller is moved to the position 3, in which the motor M is cut out. Since the brushes 12 and 15 leave the segments 10 13, an additional section of each of the condensers C C is cut in by the contact of the brushes 17 and 23 with the segments 16 and 22, and the resistances R R are cut out by the action of the segment 28. This position is shown in diagram in Fig. 7 and obviously corresponds to a slightly higher speed in the motor. In the next position, in which the brushes rest upon the line 1, the whole capacity is cut in, since all of the brushes 16 17 18 and 22 23 24; are on the segments 16 22 respectively, and in addition it will be observed that the brushes 32 and rest upon the segments 32. This makes the circuit from battery 5, through the magnet M", to the brush 32, contact 32, brush 33, and back to the battery. This energizes the magnet M" and short-circuits on itself the whole winding B in small sections instead of simply connecting together the terminals of this winding, so that its resistance is considerably diminished. This position, which is indicated in Fig. 8, is obviously the full tandem position, in which the motors will run to nearly half of their synchronous speed. In position 5 it will be noticed that the brush 3& also rests upon the segments 32, so that the magnet M is energized. This short-circuits on itself the winding A which practically cuts off current from the intermediate circuits and from the motor B, owing to the low resistance of the short circuit. It is now safe to open the intermediate circuits, which is accordingly done in the sixth position. (Illustrated in diagram in Fig. 9.) The seventh position connects the motorsin multiple. Current enters at the brush 13, as before, and passes to the segment 13, where it divides, a portion passing by brush 14, through the primary A of the motor A, and then through the brush 11 to the segment 10. A second path, however, is found from cross connection to the segment 21 and brush 21 to brush of the motor B, thence through the primary B of the motor B, out by the brush Z) to brush 19, segment 19, and cross connection to the segment 10. This connects the two motors in multiple as single-phase machines. The brush a of the motor A is connected, through the brush 20 on the controller, to the contact 20 thence through the resistance R to the contact 35", and by brush'35 to the brush a. A second circuit leads from the brush a ,through the brush 36, to segment 36, resistance R, contact 26 brush 26 to the brush A* ofthe motor A. These connections short-circuit the secondary A on itself through the resistances R R. The secondary B of the motor B is short-circuited on itself through resistances, as in the second position, since the segments 28 29 30 31 are cross-connected to the contacts 28 29 30 31. This connection is shown in Fig. 10 and is simply a multiple connection of single-phase motors, but running at half-speed with resistance in their secondaries. In such circumstances the two motors Will evidently tend to run up to synchronism by an amount depending merely on the magnitude of the resistances. In the eighth position the connections are the same, except that the resistances R R R R are displaced by short-circuiting leads. The ninth and last position (shown in Fig. 11) omits the contacts 20 20 &c., and short-circuits both secondaries on themselves by means of the magnets M M energized from the battery B through the contact 32 In this position the motors will tend to approach very near to synchronous speed.

I have illustrated my short-circuiting arrangement in Figs. 2, 3, and 4 as applied to the rotor A of Fig. 1, though a similar arrangement will obviously be applied to the stator B of the same figure. In these drawings, A A are the bars of the winding (shown developed in Fig. 4) connected together, as shown, to form an ordinary two-phase winding having free terminals at a a a a corresponding to the brushes a a a a of Fig. 1. The magnets M M, Fig. 4, serve to attract the sh ort-circuiting bar A, which is furnished with spring-contacts a9 (0, against various segments a, connected to the bars A. It will be seen that While the magnets i are deenergized the springs A Awill draw down the short-circuiting-bar A against the stops A A and the bars A will be connected like the bars of an ordinary two-phase winding. If, however, the magnets 1 M are energized, the short-circuiting bar A will be attracted and the bars will be short-circuited on themselves in pairs or single, according to connections.

In practice I prefer to replace the short-circuiting bar A by the plate A of Figs. 2 and 3, which serves thesame function,sliding directly upon the shaft of the machine. This diskA is preferably formed of two portions, an inner and an outer, insulated from each other, as shown, and is pulled away from the bars A* by springs A A.

A magnet-coil M is energized by current led in through a suitable ring A" and out by the shaft. This magnet-coil serves to energize a cup-shaped core A which attracts the inner magnetic portion of the disk A whose outer portion is preferably made of copper to short-circuit the bars A*.

The necessity for the use of condensers or equivalent devices in the independent circuits of a tandem system is explained in my prior patent, No. 587,937, dated August 10, 1897. I have shown in Fig. 1 condensers interposed directly in the circuits; but I prefer in most instances to interpose the condensers inductively. I have illustrated such an arrangement in Fig. 12, in which P P P are the three leads of the intermediate circuits of a three-phase tandem-motor system or of any other three-phase system which may obviously be substituted for the two-phase motor system shown in Fig. 1. In each one of these leads I place a very coarse transformer primary, (lettered Q Q Q, respectively.) The secondaries Q* Q Q of these transformers are connected at one end to a common point through a three-phase condenser Vand at the other end are connected to brushes 3 6 9. From intermediate points of these secondaries are taken out leads to the brushes 2 5 8 and to the brushes 1, 4, and 7. The condenserswitch is shown at X and consists of an arrangement which first connects together the brushes 1 4. 7, then the brushes 2 5 8, and finally the brushes 3 6 9. This varies the voltage upon the condenser, and thus varies the effect upon the phase displacement. This method of neutralizing or adjusting the lag in the intermediate circuits of a tandem system is not confined to the particular system shown or to any particular number of phases, but is applicable generally to tandem systems and in some respects to multiphase systems generally.

It is obvious that various changes may be made without departing from the spirit and scope of my invention. In particular I do not limit myself to the specific single-phase motor shown.

What I claim as new, and desire to secure by Letters Patent of the United States, is-

1. The method of obtaining mechanical work from the energy of a single-phase alternating current, which consists in causing, by

said single-phase alternating current, the rotation of an armature at a speed lower than synchronous rotation, converting thereby a portion of the energy of the current into mechanical work, and another portion into lowfrequency multiphase currents; transmitting said low-frequency multiphase currents to a multiphase motor, producing a rotary field in said motor by the multiphase currents, and causing by said rotary field a rotation of the second motor.

2. The method of converting the energy of single-phase alternating currents into mechanical Work, which consists in causing said currents to create a rotary field in a member of an alternating-current motor, causing said rotary field to expend its energy partly in maintaining the motor in rotation, and partly in generating in said motor multiphase alternating currents of a frequency lower than the original frequency, and utilizing part or all of the energy of said low-frequency alternating currents in causing a second alternatingcurrent motor to perform mechanical Work.

3. The method of converting the energy of single-phase alternating currents into mechanical work, which consists in causing said currents to create a rotary field in a member of an alternating-current motor, causing said rotary field to expend its energy partly in maintaining the motor in rotation, and partly in generating in said motor multiphase alternating currents of lower frequency, and utilizing part or all of the energy of said low-frequency alternating currents in causing a second motor to assist the first motor in driving its load.

4. The method of reducing the spark on opening the intermediate circuits of a tandemmotor system, which consists in short-circuiting the induced Winding of the first motor, and then opening the circuits.

In Witness whereof I have hereunto set my hand this 7th day of April, 1902.

ALBERT Gr. DAVIS. 

